Shaft kiln with orifice controlled combustion



B. L. CORSON 3,048,38l

SHAFT KILN WITH ORIFICE CONTROLLED COMBUSTION Aug. 7, 1962 Filed Nov. o, 1960 FIG.|.

2 Sheets-Sheet 1 FIG. 2.

INVENTOR: BOLTON L. CORSON BY %WW ATTYS.

B. L. CORSON Aug. 7, 1962 2 Sheets-Sheet 2 Filed Nov G z I INVENTOR: BOL TON L. CORSON ATTYS.

United States Patent Ofice &048381 Fatented Ang. 7, '1952 3,048,381 SHAFT KILN WITH ORIFICE CONTROLLED COMBUSTION Bolton L. Corson, Plymouth Meeting, Pa. Filed Nov. 10, 1960, Ser. No. 68,455 8 Claims. (Ci. 263-29) The present invention relates broadly to kilns and more specifically to shaft kilns for burning limestone and the like.

It has been found in past use of upright types of kilns which are gas fired, such as shaft kilns, when burning limestone it is very diicult to move the limestone continuously because when it becomes highly heated pieces stick to other highly heated pieces or to the walls of the kiln. Due to this condition it has become the general accepted practice in use of this type of kiln to draw treated limestone from the kiln at intervals and not continuously.

The intervals between draws may be very short or quite lengthy, such as for example, up to about four hours. The longer the interval the more pronounced are changes which take place in the calcining zone of -the kiln. When a draw takes place, pieces of limestone suddenly drop several feet down in the kiln and they are very much cooler than the pieces which were present in the same region a moment before the drop occurred. When this happens, there is a temperature difierential between that of the pieces which have dropped and that of the kiln wall in the calcining region. This temperature difference instead of being very small is very great because the kiln wall does not immediately change to any great degree. This temperature difference may be around 50 F. to 800 F. and these cooler pieces in proximity to the WallS then absorb heat from the walls which are substantially hotter.

The pieces toward the center of the kiln however, are located further frorn the end walls and therefore receive Very little heat from them. All of the heat received by these pieces is from the side walls, other than heat flowing through the kiln resulting from the burning gases. These gases, however, always tend to go` to ward the hottest portion of a kiln which is the nearest walls.

This has resulted in unsatisfactory conditions including inadequate or non-uniforrn burning of the pieces of limestone. To overcome this in the past, the temperature in the kiln has been raised but the result of this has been to increase the temperatures of the walls to such point that the refractory of the walls burns out faster, with a resultant expensive replacement and shut down time for repairs. Additionally, this increased temperature caused overburning of some of the limestone pieces. In the absence of increased heat, however, there resulted underburned pieces.

It is a principal object of the present invention to provide a kiln having a controlled gas burning combustion which overcomes the drawbacks and unsatisfactory operating conditions in prior shaft kiln constructions, and which will give more uniformity of treatment to the limestone pieces throughout the cross-section of the kiln.

A further object of this invention is to provide a kiln in which limestone is so processed as to produce less overburned and less .underburned pieces.

Another object of the invention is to provide a kiln in which greater uniformity of burning of limestone is possible and at a substantially reduced fuel cost.

An additional object of the invention is to provide a kiln which permits uniform burning of limestone with cooler kiln walls by increasingly concentrating heat from burning combustion gases from the end walls toward the center.

The objects and advantages of the invention are obtained in one embodiment thereof by so varying the size of combustion gas inlet orifices that the heat is substantially equalized across the kiln, and also contemplates the use of valves set to control gas flow or the use of constrictions in gas conduits to control gas flow.

Additional objects and advantages of the invention will be readly apparent from the following detailed description of an embodiment thereof taken together with the accompanying drawings in which:

FiG. 1 is an elevational View, partially in section, of a shaft kiln embodying the invention;

FiG. 2 is `a view taken on line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary view taken on line 3-3 of FIG. 1;

FIG. 4 is a transverse sectional view of the entire kiln taken on line 4-4 of FIG. 1;

FIG. S is an enlarged fragmentary view taken on line 5-5 of FIG. 3; and

FIG. 6 is an enlarged View taken on line 6-6 of FIG. 4.

The shaft kiln shown in the drawings is basically of a conventional Construction including a housing or outer casing lt) With a refractory liner 12, all on support means broadly shown at 14. The external configuration, as shown in FIG. 4, is substantially cylindrical. The interier of the kiln is shaped by the refractory from a widened material feed portion 16 to the calcining region 18, and is partially rectangular in cross-section, having substantially straight side walls 20, 2 2 and slightly curved end walls 24, 26. A divider and/ or support is provided at 28 of a truncated pyramidal shape which extends across the interior between the side walls 20, 22 at the lower end of the shaft. It will be noted that the refractory liner is substantially thicker at the middle sections of the side walls, and thinning as it approaches the end walls.

The burner assembly broadly includes a stepped top refracto-ry Wall or beam 30 which extends between the end walls 24, 26 and which is supported at its bottom by I-beam 32 or the like. An opening 34, of T-shape or other configuration, extends completely through the beam 30 and opens through the casing 10 at each end to the exterior. A metal support plate 36 extends along the top of the opening at the cross of the T, in the location of gas inlet nozzles as shown in FIGS. 1, 2 and 5. Spaced transverse openings 38 open outwardly from the opening 34 through each side of the beam 30 along the length thereof. Air and CO gas return ducts 40, '42 are provided which open at their upper ends into the shaft interior at 44, 46, respectively. The lower ends of the ducts 40, 42 -are connected to opposite ends of opening 34 by fittings 48, 50. Fans 52, 54 are operatively connected into the ducts which also include dampers or air inlet control valves 56, 58. Due to this arrangement the exhaust gases from the kiln which are high in CO and low in oxygen can be modified as desired, by inlet of air, and returned to the burner for proper burner control.

Headers 60-, 62 are connected to suitable sources of infiamrnable gas such as natural gas. Gas conduits 64a, 64b, 64c and 64d are connected into each header 60 and 62 with adjustable valves 66 connected in each conduit and extend inwardly into opening 34. Each of these condui-ts which extend in two groups into the interior of opening 34 have branch conduits 68 so disposed as to have one extend into each opening 38 and at their ends have nozzles or other orifice defining means. In the arrangement shown, there are different lengths of conduits having different numbers of branch conduits thereon. This arrangement provides for a high degree of control although manifestly, specifically different arrangements could be used.

Referrng now to FIGS. 3 and 4, it will be seen that the branch pipes and terminal orifices are in each opening 38 and ad'apted for direction of gas flow from opposite sides of beam 30 and along substantially the entire length thereof. In order to equalize and control the heat across the kiln in the embodiment shown, the orifices are of varying size. The size of the orifices along one side of beam 30 are schematically shown in FIG. 3 in the broken circles. These orifices are designated 70a, 70b, 70c, 70d, 70e, 70f, 70g, 7011, 701', 701', respectively and it is to be understood that those on the opposite side are identical in size and arrangement. The orifices at the end walls, namely 70a and 701', are the smallest while those at the center, namely 70e and 70f are the largest. Those in between these extremes vary in size becoming larger as they are closer to the center of the kiln.

For the desired end result, the -sizes of the various orifices will depend on kiln size but in all cases are so constructed that the central ones are the largest, and the end ones the smallest. They can vary in substantially a straight line arithmetic progression or otherwise as determined for best Operating results. The valves also permit control of the gas flow in different regions of the kiln. While in the drawings, an even number of nozzles or orifices has been shown, this can be varied so as to use an uneven number with the largest orifice at the center of the kiln and succeeding ones thereof toward the end walls decreasing in size.

It will accordingly be seen that the present invention teaches a burner Construction and arrangement which overcomes drawbacks of previous shaft kilns and results in greater unformity of treatment of the lmestone pieces processed in the kiln. While one embodiment of the invention has been shown and described for illustration of a workable embodiment, manifestly other types or arrangements which can control gas flow *across the interior of the kiln are contemplated within the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a shaft kiln and the like for burning of lmestone, a refractory liner definng a vertical material -treating shaft of generally rcctangular interior cross-section conguration having opposed end and side walls, the refractory liner being substantially thicker at the middle sections of said side walls `and thinning as it approaches the end walls, a material burner assembly extending substantially across the interior horizontal length of said shaft between the end walls, and means operatively associated with said burner assembly for increasingly concentrating heat therefrom from the end walls toward the center for maximum heat at the shaft center.

2. In a shaft kiln and the like for burning of limestone, a refractory liner defining a vertical material treating shaft of generally rectangular interior cross-section configuration having opposed end and side walls, the refractory liner being substantially thicker at the middle sections of said side walls and thinning as it approaches the end walls, gas burner means extending substantially across the interior horizontal length of said shaft between the end walls, said gas burner means including a gas conduit having gas outlet orifices spaced along the length thereof, said orifices varying in size from a largest opening at the center of the shaft to ones of smallest openings in proximity to the inner walls of said shaft.

3. In a shaft kiln as claimed in claim 2, the size of said orifices varying in substantially a straight line progresson.

4. In a shaft kiln as claimed in claim 2, said gas conduit extending in 'a direction between said end -walls and substantially parallel to said side walls and centrally thereof.

5. In a shaft kiln as claimed in claim 2, vertically disposed air and combustion gas return ducts exteror of said shaft having their inlet ends opening into said shaft at a level adapted to be above the level of material being burned in said kiln and their outlet ends opening into said shaft in proximity to said burner means, fans in said ducts and air inlet control means in said ducts for varying the air content of gases returned to said kiln.

6. In a shaft kiln as claimed in claim 1, said burner assembly comprisng gas burner means including at least one gas conduit having orifices spaced 'along the length thereof, and means associated with said conduit whereby gas distribution flowing from said orifices can be controlled so that a maximum burning will occur in proximity to the center of the kiln and diminishing towards the end walls of the kiln.

7. In a shaft kiln as claimed in claim 6, wherein the gas distribution control means conprises adjustable valves in said conduits.

8. In a shaft kiln as claimed in claim 6, wherein the gas distribution control means comprises gas flow constrictions in said conduits.

References cited in the file of this patent UNITED STATES PATENTS 2,108,l18 Greenwalt Feb. 15, 1938 2,409,527 Azbe Oct. 15, 1946 2,933,297 Erasmus et al. Apr. 19, 1960 FOREIGN PATENTS 174,360 Germany Sept. ll, 1906 

